Kenji Saito

Professor of Physics


  • Joined the laboratory in April 2012
  • Accelerator physics
  • Contact information

Education and training

  • BS, Mathematics and Physics, Ritsumeikan University, 1977
  • PhD, Nuclear Physics, Tohoku University, Japan, 1983


The accelerator is the base tool for nuclear physics, high energy physics, light sources, medical applications, and so on. Superconducting Radio Frequency (SRF) Systems are an application of microwave acceleration for ion beams. The principle is the same as normal conducting RF system, but SRF systems use superconducting technology, which allows high-quality beam acceleration with very high efficiency. It is a key technology for current world-wide accelerator projects for nuclear science and high energy physics. SRF systems are a state-of-the art technology to open new areas of particle physics. The FRIB Project at MSU utilizes this system for a major part of the accelerator. I joined FRIB graduate school education program serving as the FRIB SRF development manager since 2012.

The main part of an SRF system is the so-called cryomodule and RF system. A cryomodule consists of a cryostat and SRF cavities included therein. Ionized beam is accelerated by SRF cavities, which is made of superconducting material and cooled by liquid helium at below 4.2K. A cryostat is a kind of Thermos bottle to keep SRF cavities at such a low temperature. Niobium material has been utilized for SR cavities, which has high-quality superconducting features: higher superconducting transition temperature Tc=9.25K and higher thermodynamic critical field Hc=200mT. Niobium has a good forming performance to fabricate cavities. Development of high-quality niobium is always a concern and I have been working on high purity niobium material. My latest concern is single crystalline niobium ingot or other new materials. In RF cavity design it is very important to have an excellent SC cavity performance, which has to be simulated intensively by specific computing cords. I have developed a high gradient SRF cavity shape with an acceleration gradient > 50MV/m and demonstrated the high-performance, which is a world record so far. This activity will applied other new SRF systems.

The SR cavity performance subjects to very shallow surface characteristics where the RF surface current flows. Particle/defect free clean surface is especially crucial. Chemical clean surface preparation and clean assembly technology are key technologies. I have developed electropolishing method for elliptical shaped the SRF cavity and confirmed it is the best process for high gradient cavities. This technology will be applied to low beta cavities and push the gradient in order to make the SRF system more compact.

Cryostat design includes lots of engineering and material issues. We are investing a lot on this subject in ongoing FRIB cryomodule. The RF system is another exciting place to study. Concerning SRF, high-power coupler is an important issue to develop. The design of multipacting free high power coupler structure and cleaning technology, TiN coating technologies, would make for a great theme for a thesis. Thus the SRF systems cover various sciences and super-technologies: electromagnetic dynamics, superconducting material science, plastic forming technology, ultra-clean technology, ultra-high vacuum, cryogenics, RF technology, mechanical/electric engineer. The SR system is an exciting place to study. Any students from physics, chemistry, materials, and mechanical/electric engineering are welcome to join this project.

Scientific publications